1. Field of the Invention
The present invention relates to an interleaved bridgeless power factor corrector and a controlling method thereof, and more particularly, to a low-loss, high-power-density power factor corrector and a controlling method thereof, which can be applied to various kinds of power supply products, especially those applications which require high power density and medium-to-high power output applications in a limited space.
2. Description of the Prior Art
A conventional AC to DC converter comprises a rectifier and a DC converter, as shown in FIG. 1, the rectifier rectifies the current by using four diodes connected in a bridge form, that is, the rectifier acts as a bridge rectifier; the DC converter is usually a boost converter to achieve high power factor and to reduce total harmonic distortion (THD). In order to meet demands of new applications and various power regulations and performance requirements, all kinds of power supply topologies and controlling method are proposed, such as a bridgeless power factor corrector (PFC) and an interleaved PFC. A bridgeless PFC eliminates the need of the bridge rectifier in the traditional power supply topology, more precisely, it uses two active switches (such as POWERMOSFET, IGBT, BJT) to replace the two low side diodes in the bridge rectifier and to form a boost converter with the cascaded inductor of the input AC power supply, as shown in FIG. 2A. Another bridgeless PFC uses two active switches to replace diodes of one branch of the bridge rectifier, as shown in FIG. 2B, the two diodes on the right branch are used for determining a flow of the current, and the two active switches and the inductor on the left branch form a boost converter to meet the requirements of high power factor and low THD and to provide feedback to the bridgeless PFC for controlling the active switches, thereby achieving the same performance as that of the traditional converter. Besides, by using active switches to replace the passive switches (diodes), the forward voltage drop loss caused by the diodes no longer exists, and only the conduction loss of the active switches remains; since the conduction loss is far less than the forward voltage drop loss in most applications, therefore the bridgeless PFC can provide better power conversion efficiency.
Another hot power supply topology is the interleaved power factor corrector, as shown in FIG. 3, as compared with the bridgeless PFC, the interleaved power factor corrector are more popular and have been applied in all kinds of high power density DC to DC converters, such as the VRM power supply for the CPU and high power communication applications. The interleaved power factor corrector are constructed by connecting more than one power supply converter in parallel and synchronizing the switching frequency of each converter with a respective phase delay, wherein the phase delay is determined by the number of converters in parallel (that is, phase delay is 360/n, n is the number of converters), the cancellation effect of the input/output current due to interleaved switching signals could reduce the current ripple as the number of converters in parallel increased and obtain frequency multiplication, which help to reduce the size of the output filter and the front end EMI filter, meanwhile, distributing the total power in n sets of converters could facilitate better heat dissipation and efficiency; based on this principle, the interleaved power factor corrector are constructed by connecting more than two sets of boost converter in parallel and using a feedback mechanism to achieve high power factor conversion.
Therefore, the bridgeless PFC and the interleaved power factor corrector can have their respective advantages and application fields, it is desirable to combine the advantages of both to provide a power factor corrector having low loss and high power density and to maximize the possible applications for the converter.
In view of the deficiencies of the prior art techniques, after years of constant researches, the inventor has successfully proposed an interleaved bridgeless power factor corrector and a controlling method thereof in the present invention.